Curable silicone compositions that can be cured by a hydrosilylation reaction are used as coating agents or protective agents for optical semiconductor elements of semiconductor devices such as photo couplers, light-emitting diodes, solid-state imaging devices, etc. Such curable silicone compositions can be exemplified, e.g., by a curable silicone composition comprising at least an organopolysiloxane having in one molecule at least two alkenyl groups where at least 20 mole % of all silicon-bonded organic groups are aryl groups, an organopolysiloxane that contains silicon-bonded hydrogen atoms, an organopolysiloxane where in one molecule at least 5 mole % of all silicon-bonded organic groups are alkenyl groups, at least 5 mole % are aryl groups, at least 5 mole % are alkoxy groups, and at least 5 mole % are epoxy-containing organic groups, and a hydrosilylation catalyst (see Japanese Unexamined Patent Application Publication No. 2007-327019), or a curable silicone composition comprising an organopolysiloxane where in one molecule at least 0.5 mole % of all silicon-bonded organic groups are alkenyl groups, and at least 25 mole % are aryl groups; an organopolysiloxane having in one molecule on average at least two silicon-bonded aryl groups and on average at least two silicon-bonded hydrogen atoms, and a hydrosilylation catalyst (see Japanese Unexamined Patent Application Publication No. 2008-1828).
Since hardness of cured products obtained from the aforementioned curable silicone compositions can be reduced under the effect of heat, these compositions may have stress relaxation effects to semiconductor elements when these composition are used as coating or protective agents for semiconductor elements. However, the proportion of the reduction is not sufficient.
It is an object of the present invention to provide a cross-linkable silicone composition that can be cross-linked by a hydrosilylation reaction and that forms a cross-linked product which is a solid body of high hardness at room temperature and becomes significantly soft or liquefied at high temperature. It is another object of the invention to provide a cross-linked product that is solid and has high hardness at room temperature and that becomes significantly soft or liquefied at high temperature.